In recent years, ongoing increase to capacity and speed is required in response to implementation of broadband to mobile communication services. In this regard, a 3rd-generation mobile communication system represented by W-CDMA (Wideband Code Division Multiple Access) or the next-generation mobile communication system, which is an alternative to a 3.5th-generation mobile communication system, has been commercialized all over the world. Also in Japan, frequency assignment to a 3.9th-generation mobile communication system, which is positioned as a mobile communication system leading to a 4th-generation mobile communication system, has begun. In the 3.9th-generation mobile communication system, LTE (Long Term Evolution) is the most powerful candidate for a standard leading to the 4th-generation mobile communication system.
In the LTE, OFDMA (Orthogonal Frequency Division Multiplexing Access) is adopted for downlink communication toward a radio terminal from a radio base station, and SC-FDMA (Single Carrier Frequency Division Multiplexing Access) is adopted for uplink communication toward the radio base station from the radio terminal. In these multiplexing methods, user multiplexing is achieved by arranging a radio resource in the two dimension of frequency and time.
A frequency band, which is a downlink radio resource, is divided in units of a resource block (RB). The RB includes a control information channel (PDCCH: Physical Downlink Control CHannel), which is a time slot as a radio channel for downlink control information transmission, and a shared data channel (PDSCH: Physical Downlink Shared CHannel) which is a time slot as a radio channel for transmitting downlink user data.